Method and Audio Noise Suppressor Using Nonlinear Gain Smoothing for Reduced Musical Artifacts

1. A noise suppressor comprising: a band extractor adapted to separating a frequency domain input by frequency band; at least one per-band unit comprising: a noise estimator coupled to receive a per-band output of the band extractor, a signal to noise ratio (SNR) computation unit coupled to receive an output of the noise estimator and the per-band output of the band extractor and to provide a current SNR, a histogramming unit coupled to provide a histogram of the current and past SNRs, a gain-curve updater configured to derive a gain curve from the histogram of the current and past SNRs, a raw-gain finder configured to use the gain curve and the current SNR to determine a raw gain, a post-filtering unit coupled to receive the raw gain and to provide a filtered gain, and a variable gain unit coupled to receive the per-band output of the band extractor and apply the filtered gain to provide a band-specific gain-adjusted, signal; and a combiner configured to combine the band-specific, gain-adjusted, signals from each per-band unit into a noise-reduced frequency-domain signal.

2. The noise suppressor of claim 1 wherein the post-filtering unit of the at least one per-band unit further comprises a low-pass finite-impulse-response digital filter.

3. The noise suppressor of claim 2 the at least one per-band unit further comprising a multiband smoother that performs a weighted-average of a current-band and adjacent-band intermediate gains to provide the filtered gain.

4. The noise suppressor of claim 3 further comprising a frequency domain converter adapted to perform a fast Fourier transform (FFT), discrete Fourier transform (DFT) or discrete cosine transform (DCT) to translate an input into the frequency domain input.

5. The noise suppressor of claim 1 the at least one per-band unit further comprising a multiband smoother that performs a weighted-average of a current-band and adjacent-band intermediate gains to provide the filtered gain.

6. A method of noise suppression comprising: separating a frequency domain input by frequency band into frequency band signals; for each frequency band signal, estimating noise of the frequency band signal, deriving a signal to noise ratio from the estimated noise and the frequency band signal to provide a current SNR, histogramming the SNR to provide a histogram of the current and past SNRs, updating a gain curve from the histogram of the current and past SNRs, finding a raw gain using the gain curve and the current SNR, filtering the raw gain to provide a filtered gain, and applying the filtered gain to the frequency band signal to provide band-specific gain-adjusted, signals; and combining the band-specific, gain-adjusted, signals into a noise-reduced frequency-domain signal.

7. The method of claim 6 wherein filtering the raw gain includes low-pass filtering.

8. The method of claim 7 wherein filtering the raw gains of a first frequency band of the frequency bands includes performing a weighted-average of a current-band and adjacent-band intermediate gains.

9. The method of claim 8 further comprising performing a fast Fourier transform (FFT), discrete Fourier transform (DFT) or discrete cosine transform (DCT) to translate an input into the frequency domain input.